Field of the Invention
The present invention relates to a toner producing apparatus, and a toner producing method.
Description of the Related Art
In a method of producing fine powder with mills, impact plate type mills, counter jet mills, and mechanical mills may be included as examples of mills that can produce fine powder having an average pulverized particle diameter of 4 μm to 10 μm at a production output of 150 kg/h to 200 kg/h if raw powder material having a particle diameter of approximately 30 μm is fed into the mills.
The impact plate type mills have such a feature that accelerates raw powder material by jet streams, and forces the accelerated raw powder material to collide against an impact plate so as to pulverize the raw powder material. The IDS series of Nippon Pneumatic Mfg. Co., Ltd. may be included as an example of the impact plate type mills, for example.
The counter jet mills have such a feature that accelerates raw powder material with counter jet streams, and allows the accelerated raw powder material to collide against each other. PJM-I of Nippon Pneumatic Mfg. Co., Ltd., Micron Jet Mill and Counter Jet Mill of Hosokawa Micron Corporation, and Cross Jet Mill of Kurimoto Ltd. may be included as examples of the counter jet mills, for example.
The impact plate type mills and the counter jet mills have such a configuration that injects raw powder material along with ultra-high speed jet streams, and allows the raw powder material to collide against the impact plate, or collide against each other, thereby pulverizing the raw powder material.
The impact plate type mills and the counter jet mills require great amount of air in order to accelerate the raw powder material using jet streams. Consequently, they have problems such as great electricity consumption, high energy cost, and great impact on environment.
Meanwhile, in the light of reduction in energy cost and impact on environment, the mechanical mills have been used as mills more efficient than the impact plate type mills and the counter jet mills. The mechanical mills feed raw powder material into gaps between rotors rotating at a high speed and stators so as to pulverize the raw powder material. Hence, the mechanical mills require no jet streams, and consume almost no compressed air during pulverizing the raw powder material. Accordingly, the mechanical mills can produce fine powder with saved energy.
As an example of the mechanical mills, there has been suggested a mechanical mill that includes a pulverizing chamber including a rotor and a stator disposed with a predetermined gap therebetween, and pulverizes raw powder material fed in the pulverizing chamber into fine powder through collision among the rotor, the stator, and the raw powder material accompanied by the rotation of the rotor (see Japanese Patent Application Laid-Open (JP-A) No. 2010-51875, for example).
Not only such mechanical mills, but also any mills using rotors can produce fine powder with reduced energy.
Raw powder material to be fed in a mill using a rotor is produced such that resin, colorant, and others are kneaded, for example, and furthermore raw powder material may be roughly pulverized if necessary. The above kneading process is carried out by a kneading machine. For example, in producing raw powder material for electrophotographic toner, a kneading machine having a crew is generally used. Such a kneading machines having a screw includes the screw and a casing disposed at the outer periphery of the screw. The screw has helical projections around its shaft. The screw or the casing is provided with pins that are column-like projections. Such a kneading machine having the screw efficiently carries out kneading operation in cooperation with the projections of the screw, and the pins.
During producing raw powder material through a kneading machine having a screw, metallic foreign matters may be mixed in the raw powder material resulted from the screw and the pins. High pressure is generated inside the kneading machine during the kneading operation. Such high pressure is likely generated between the helical projections of the screws, between the pins, and between the helical projections and the pins, etc. Hence, the helical projections or the pins become broken due to fatigue, impact, or the like because of such high pressure, resulting in generation of the metallic foreign matters. It has also been known that, for example, fatigue fracture is caused to a screw in a kneading machine (see JP-A No. 2009-131965, for example). Broken pieces of the screw resulted from the fatigue fracture become the above metallic foreign matters.
Contamination of metallic foreign matters in raw material powder causes the following problems. One is that if the metallic foreign matters along with the raw powder material are fed in a mill, the metallic foreign matters collide against a rotor of the mill, which may case breakage of the rotor. The metallic foreign matters held in a gap between the rotor and stator may cause such a problem that the metallic foreign matters stop the mill. Another is that the metallic foreign matters mixed in the raw powder material are pulverized by the mill, resulting in contamination of fine pieces of the pulverized metallic foreign matters in finished toner. In this case, such a problem may be caused that the finished toner containing the fine pieces of the metallic foreign matters causes damage on a photoreceptor in an image forming process.
A method of providing a filter for removing the metallic foreign matters in conveyance piping may be included as an example of conventional methods of removing the metallic foreign matters, for example. Unfortunately, mills that produce fine powder have so small gaps inside the mills that the raw powder material is needed to be supplied at high static pressure. Particularly in the mills using rotors, the raw powder material passes through extremely fine gaps, so that it is difficult to supply the raw powder material at low static pressure, and thus high static pressure is inevitably required in conveyance piping for supplying the raw powder material. Consequently, no filter can be installed in the conveyance piping for supplying the raw powder material into the mills.
Accordingly, it has been desired to provide a toner producing apparatus capable of separating metallic foreign matters from raw powder material of toner before the raw powder material of toner is pulverized by a mill using a rotor, capable of preventing the mill using a rotor from being damaged and stopped, and also capable of preventing produced toner from causing damage on a photoreceptor.